How does the FetchMode work in Spring Data JPA

Question

I do have a relation between three model object in my project (model and repository snippets in the end of the post.

When I call PlaceRepository.findById it does fire three select queries:

("sql")

1. SELECT * FROM place p where id = arg
2. SELECT * FROM user u where u.id = place.user.id
3. SELECT * FROM city c LEFT OUTER JOIN state s on c.woj_id = s.id where c.id = place.city.id

That's rather unusual behavior (for me). As far as I can tell after reading Hibernate documentation it should always use JOIN queries. There is no difference in the queries when FetchType.LAZY changed to FetchType.EAGER in the Place class (query with additional SELECT), the same for the City class when FetchType.LAZY changed to FetchType.EAGER (query with JOIN).

When I use CityRepository.findById suppressing fires two selects:

1. SELECT * FROM city c where id = arg
2. SELECT * FROM state s where id = city.state.id

My goal is to have a the sam behavior in all situations (either always JOIN or SELECT, JOIN preferred though).

Model definitions:

Place:

@Entity
@Table(name = "place")
public class Place extends Identified {

    @Fetch(FetchMode.JOIN)
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id_user_author")
    private User author;

    @Fetch(FetchMode.JOIN)
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "area_city_id")
    private City city;
    //getters and setters
}

City:

@Entity
@Table(name = "area_city")
public class City extends Identified {

    @Fetch(FetchMode.JOIN)
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "area_woj_id")
    private State state;
    //getters and setters
}

Repositories:

PlaceRepository

public interface PlaceRepository extends JpaRepository<Place, Long>, PlaceRepositoryCustom {
    Place findById(int id);
}

UserRepository:

public interface UserRepository extends JpaRepository<User, Long> {
        List<User> findAll();
    User findById(int id);
}

CityRepository:

public interface CityRepository extends JpaRepository<City, Long>, CityRepositoryCustom {    
    City findById(int id);
}

Answer 1

I think that Spring Data ignores the FetchMode. I always use the @NamedEntityGraph and @EntityGraph annotations when working with Spring Data

@Entity
@NamedEntityGraph(name = "GroupInfo.detail",
  attributeNodes = @NamedAttributeNode("members"))
public class GroupInfo {

  // default fetch mode is lazy.
  @ManyToMany
  List<GroupMember> members = new ArrayList<GroupMember>();

  …
}

@Repository
public interface GroupRepository extends CrudRepository<GroupInfo, String> {

  @EntityGraph(value = "GroupInfo.detail", type = EntityGraphType.LOAD)
  GroupInfo getByGroupName(String name);

}

Check the documentation here